1. Field of the Invention
This invention relates to a co-catalyst component used in the production of .alpha.-olefin polymer, and more particularly to a process for producing an .alpha.-olefin polymer quite low in the contents of catalyst residue and amorphous polymer and excellent in mechanical properties and processability which comprises using a catalyst system comprising a solid catalyst component containing at least magnesium, titanium, halogen and ester compound and a specified co-catalyst component.
2. Description of the Prior Art
As the method for producing a polymer of .alpha.-olefin such as propylene, butene-1 and the like, the method using the so-called Ziegler-Natta catalyst comprising a compound of transition metal belonging to Group IV-VI of the periodic table and an organometallic compound of a metal belonging to Group I-III of the periodic table is well known. Particularly in the industrial production of .alpha.-olefin polymers, solid catalysts such as titanium type catalyst comprising titanium trichloride as transition metal compound and titanium-magnesium composite catalyst are widely used today.
In the titanium trichloride type solid catalyst, halogen-containing aluminum compound such as diethylaluminum chloride is used as the organometallic compound of the co-catalyst. In such a polymerization process, catalyst residue such as halogen originated from co-catalyst remains in the formed .alpha.-olefin polymer, which makes various troubles on stability, processability, etc. of the resulting .alpha.-olefin polymer. Accordingly, a particular equipment must be provided for removing the catalyst residue and stabilizing the polymer.
This disadvantage can be overcome either by enhancing catalyst activity expressed by the weight of resulting .alpha.-olefin polymer per unit weight of catalyst or by using a catalyst containing a small amount of element making the cause of catalyst residue. By taking these measures, the above-mentioned equipment for removing catalyst residue can be made unnecessary and production cost of .alpha.-olefin polymer can be reduced.
On the other hand, in the case of titaniummagnesium composite solid catalyst, there is used a ternary catalyst system to which are separately added a halogen-free organoaluminum compound such as triethylaluminum as organometallic compound of co-catalyst and an electron donor for improving stereospecificity of resulting .alpha.-olefin polymer In such a polymerization process, no halogen originated from co-catalyst is contained in the resulting .alpha.-olefin polymer However, such a catalyst is insufficient in catalytic activity, so that a catalyst residue originated from solid catalyst remains in the polymer. That is to say, the above-mentioned problems are not completely solved in this process, too.
Further, in any of the above-mentioned solid catalysts, production of .alpha.-olefin polymer is accompanied by formation of amorphous polymer as a by-product in addition to the highly stereospecific .alpha.-olefin polymer having a high industrial value. This amorphous polymer is poor in industrial value, and it exercises greatly adverse influences upon the mechanical properties of processed articles, such as film, fiber and the like, of the .alpha.-olefin polymer. In addition, the formation of the amorphous polymer results in a loss of starting monomer, and the formation of amorphous polymer necessitates to provide a particular equipment for removing the amorphous polymer, which is quite disadvantageous from the industrial point of view. Thus, the catalyst system used in the production of .alpha.-olefin polymer must be a catalyst system which yields no amorphous polymer at all or yields only a very slight quantity of amorphous polymer.